Comminuted ferromagnetic cores



May 20, 1952 A. w. FRIEND ET AL 2,597,236

COMMINUTED FERROMAGNETIC CORES Filed Oct. 24, 1947 DAMPER TRANSFORMER ems 0F DEFLELWUA/ HOR/ZONML 4 POWER 007 07 I TUBE was 2 i i -1 l r: j Z 1 I LOW L055 HURIZONML) IMAGE MOIDED IRON REFLECTION REPRODl/C'ING POWDER CORE COIL (An/ 055? DEFLEC'T/ON YO/(E CORE x UNIREATED c o/zs EFFECT OF HEAT murmur 2F gggggflolz YO/(E can: 30- N WNW #54750 Af sow-900% DFFZECf/UIV (U/L9 I, FOR ,5 MINUTES HEATED 47800 2900 1 FOR JOMINUIFS MEASURED VAL LIES 0F 0 /0 2 '3'4'! 'siiw 2' '3' 1 ia'ilo FREQUENCY (crass/95c.)

. lNVENTORS ALBERT w. FRIEND ARTHUR T. HARDING Patented May 20, 1952 COMMINUTED FERROMAGNETIC corms Albert W. Friend, Princeton, and Arthur T.

Harding, Audubon, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application October 24, 1947, Serial No. 781,804 4 Claims. (01. 148-4) Our. present invention relates generally to a novel treatment of comminuted ferromagnetic cores and the improved product resulting therefrom, and more particularly to a novel method of altering the loss characteristic of such cores.

In certain applications of comminuted ferromagnetic core materials, as core structures in electromagnetic systems, it is often desirable to control the energy losses in the core material thereby to achieve a desired degree of damping effect. It is at the same time desirable to maintain the apparent permeability sensibly constant, 1. e., changes in the order of :2 or 3%.

It may, therefore, be stated to be an important object of our present invention to provide a novel method of altering or controlling the energy storage factor Q of coils or inductances utilizing comminuted ferromagnetic core material with a net result such that the energy losses in the core structure are increased to any desired degree while the eiiective permeability is not sensibly decreased, or may even increase slightly at certain frequencies.

It is another important object of our present invention to produce the aforesaid efiects by including in the comminuted ferromagnetic core material mixture at relatively small amount of resinous or carboniferous binder material which is converted in varying degrees to finely divided carbon between the magnetic particles bymeans of a heat treating step p ovided at the end of the normalcuring step, the aforesaid carboni zation oi. the binder materials being accompanied by sintering if a sufficiently high temperature is employed. t

It can be stated that it is a further object of our invention to provide a method for increasing and controlling the energy losses of high permeability powdered-iron cores which have been molded under high molding pressure, whereby such cores may be utilized as deflection yoke cores for an image reproducing cathode raytube thereby to provide easier attainment of the required picture deflection linearity when an economical damping device is used for the horizontal deflection coils.

A more specific object oi our invention is to make possible the provision of wrinkle-free scanning by a circuit utilizing low cost components thereby to lower the ,cost of production and as- "sembly of a television receiver.

While we have indicated and described a .sys-

tem for carrying our invention into effect, it will .be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many 'under very high molding pressures.

netic material.

modifications may be made without departing from the scope of our invention.

In the drawing:

Fig. 1 schematically shows the portion of a television receiver associated with the horizontal deflection coils;

Fig. 2 shows a section of a deflection yoke core constructed in accordance with our invention;

and

Fig. 3 graphically illustrates the effect produced by the treatment of the present invention.

There has been disclosed by Albert W. Friend in application Serial No. 619,870 filed October 2, 1945, now U. S. Patent No. 2,513,160, issued June 27, 1950, and more particularly in Fig. 5 thereof, a cathode ray beam deflection circuit adapted for an image reproducing cathode ray tube of a television receiver. In that application there has been disclosed and claimed an output coupling transformer feeding horizontal deflection coils of the deflection yoke, the transformer core being coniposed of powdered or comminuted iron or other finely divided ferromagnetic material.

The major component parts of the kinescope in television receivers are the horizontal defiection transformer and its associated deflection yoke, and that these devices have been responsible for at least half the energy loss in many systems. While proposals have been made to decrease such energy losses, the development of the low-cost. high-permeability molded iron dust core solved the problem. Low cost sponge iron and electrolytic iron powders mixed with very small amounts of resinous binders are pressed into core shapes pressures between 15 and tons per square inch have been used to reduce the inter-particle insulation to a minimum thickness thereby to avoid a seriously detrimental amount of eddy currents involving more than one particle of the ferromag- In this way large magnitudes of permeability increase were secured. Such lowloss, high-permeability molded iron powder cores have been used for both the horizontal deflection transformer and the deflection yoke. V

However, in the use of such low-loss, highpermeability molded iron cores, it may become desirable to control the energy losses in the core material so as to achieve a desired degree of damping effect. In order more clearly to explain the present invention reference. is made to the schematic circuit shown in Fig. 1. It is to be clearly understood, however, that our invention is in no way limited or restricted to treatment of the deflection yoke core of a television Molding receiver. The present method, and product resulting therefrom, will be found of value and utility in any application where it is desired to increase the energy losses in the comminuted ferromagnetic core structure in a controlled manner without sensibly decreasing the permeability.

In Fig.1 there is schematically shown a cathode ray beam deflection circuit including a. power output tube I adapted to deliver cyclically varying current. A portion of each cycle of the current varies in a substantially linear manner with respect to time; the waveform is essentially sawtooth. The output current is delivered to a pair of cathode ray beam deflection coils' 2, the horizontal deflection coils, through the coupling transformer 3 whose core 4 may be constructed as described in the aforesaid Friend application. The primary winding 5 'of the transformer 3 is connected in the plate circuit of tube l, the secondary winding 6 is connected at its opposite ends to the respective ends of deflection coils 2. A damper tube 1, a diode in the present case, is connected across the winding 6, the diode anode 8 being connected in series with the resistance-condenser combination 9. Damper diode 1 together with network 9 prevent oscillations in the circuit by acting as a switch which closes at the end of the return, or snap-back, portion of each cycle of the sawtooth current wave, 1. e., at the beginning of each deflection cycle.

The switching operation of diode 7 causes a current to flow therethrough which is of such a wave form as to assist the power tube in producing the desired linear current variation through the deflection coils. The operation of such a damper tube is set forth in U S. Patent No. 2,309,672 granted on February 2, 1943 to Otto H. Schade. The coils 2 form part of a yoke assembly encircling the neck ID of kinescope tube I I. The latter may be of any type of image reproducing cathode ray tube. The yoke c'ore l2 in Fig. l is a schematic representation, and its actual configuration may be as shown at l2 in Fig. 2. The latter is a ring, being shown as a median section in Fig. 2, and encircles the neck Ill. The deflection coils are wound on the core l2.

It is sufiicient for the purposes of our present patent application to point out that the instantaneous angle of deflection of the cathode ray scanning beam of kinescope H is a function of the instantaneous strength of the magnetic deflecting field. The latter depends on the amplitude of the sawtooth current wave, and any change in peak amplitude of the sawtooth wave produces a change in the size of the image raster scanned by the cathode ray beam. The use of powdered or comminuted ferromagnetic material for the construction of the transformer core 4 and deflection yoke core [2 has many advantages, and these have been pointed out in the aforesaid application.

In summary it can be said that costs are lowered; molding permits wide choice of core shapes; maximum permeability is attained due to selection of particle size distribution; low losses of powdered iron material in the television frequency range cause less heat loss; efficiency of energy transfer is improved; acoustic energy radiation is decreased. High molding pressures between 15 and 60 tons per square inch are employed to provide low-loss, high-permeability cores having the aforesaid advantages.

molding pressure reduces the inter particle insulation to a minimum thickness thereby to avoid a seriously detrimental amount of eddy currents involving more than one particle of the ferromagnetic material. An additional purpose in using the high molding pressure is to deform the individual particles into new shapes providing more complete interlocking of theparticles and eliminating voids. As a compromise between electrical, magnetic and mechanical properties, there was selected a figure of 0.75% resin (by weight) for the optimum amount of resin bonding -material to use. Low cost sponge iron and electrolytic iron .powders have been used, and

an each case the maximum particle thickness was about 0.005 inch.

In accordance with our present invention we provide 'a heat'treating method for increasing and controlling the energy losses of the yoke core 12' shown in Fig. 2; to provide easier attainment of the required picture linearity when the relatively cheaper diode damper device 1 is used instead of a triode damper. In the specific case shown in Fig. 1 this result is achieved at the expense of reducing the total available deflecting capability of the system. For most television receiver construction it is desirable, in general, to utilize a predetermined heat'treatment after the normal curing process to produce a required value of deflection yoke core loss at the specified frequencies involved so that damping of the transient effects may be effective to an adequate extent by economical types of electronic devices. This makes possible the production of adequately linear wrinkle-free scanning by a circuit utilizing low cost parts without adding extensive external loss correcting circuits of a frequency varient nature. The 'net result of the present heat treatment is that the energy losses in the deflection yoke core structure are increased to any desired degree, and that deflection permeability is not sensibly decreased, or may even increase slightly at certain frequencies. 7

It is possible to produce the desired effects in core l2 by including in the core mixture the normal small amount of resin binder materials. As stated previously, the optimum amount of resinous material would be about 0.75% by weight. While any suitable thermo-setting resinous or carbonaceous material may be used as a binder, we have used the phenol formaldehyde type. Specifically, for example, we used a combination of two such resins; one was a liquid resin containing about solids, while the other was a finely divided solid resin. The lowloss core is molded under high pressure as previously described, and then cured in the normal and usual way. The resulting low-loss core is subsequently subjected to an extra heat treating step for a predetermined period of time. The purpose of the heat treatment is to convert the resin material in varying degrees to finely divided carbon. This carbon will exist between the magnetic particles. 1

More specifically the temperature of the heat treatment is elevated to approximately 800 to 900 Fahrenheit for the period of time deter mined to yield the required degree of carbonization of the resin material. If a sufiiciently high temperature is employed it is possible to provide some sintering action so as to tie together some of the metallic particles.

In Fig. 3 we have shown the effect of heat treatment of the deflection yoke core on the O. of the horizontal deflection coils 2. The brokenline curve A shows the relatively high 'Q value secured with the untreated low-loss core. The solid line curve B illustrates the appreciable energy losses introduced into the core structure when the core is heat treated at 800 to 900 Fahrenheit for fifteen minutes. The Q of the deflection coils 2 has dropped almost 50%. Solid line curve C shows the additional energy losses secured by extending the heat treatment to thirty minutes. In this way the increased losses introduced in the core I2 are utilized to augment the action of the damping diode 1 on the transient effects. It may be seen from an examination of the curves of Fig. 3 that the length of the period during which heat is applied to the core will determine the magnitude of the losses which are imparted to the core. In general, it may be stated that when the core is subjected to heat treatment in an oven it will require, on the average, approximately five minutes for the heat to uniformly penetrate the core, so that the carbonization of the binding material and/or the sintering of the magnetic particles may be uniformly accomplished. Obviously, if other well known methods of heating the cores are employed, some variation in this minimum time will be required. Furthermore, the configuration of the core itself will have a bearing on the minimum time required to uniformly penetrate the core.

It is to be clearly understood that our present invention is not restricted to heat treatment of deflection yoke cores specifically. On the contrary it is of wide application, and may be used wherever it is desirable to control the energy losses in comminuted ferromagnetic cores so as to achieve a desired degree of damping effect. It is at the same time desirable to maintain the apparent permeability sensibly constant. It is emphasized that the effect of the heat treatment is to increase the conductive paths between the ferromagnetic particles in two ways. In the first place resin binder particles are converted to finely divided carbon particles or to a matrix of carbonized material functioning as a conductive path. Secondly, by providing sufficient heating actual sintering of the ferromagnetic particles takes place. It will be understood, of course, that the degree of temperature employed and the length of heat treatment will depend upon the magnitude of energy losses desired in a given ferromagnetic core structure.

The cores after heat treatment contain an excess or residue of carbon. Analysis of the finished cores indicates 0.67% carbon remaining, and since the heat treating temperature (900 F.) exceeds the decomposition temperature of the resin the residual carbon must be in the free, or uncombined, state. That sintering occurs during the heat treatment of the cores is shown by the fact that the heat-treated core is much stronger mechanically than the core is after curing, but before heat treatment, notwithstanding the fact that heat treatment destroys the binding resin.

In addition to the sintering during heat treatment considerable oxidation of the iron particles occurs, and this tends to increase the losses in the cores. We are not at present, prepared to explain the nature of the losses occurring through oxidation of the iron particles. Such losses have obtained experimentally on numerous occasions.

All comminuted ferromagnetic cores are molded under a relatively high molding pressure. but this present heat treatment method may be used, if

desired, with any and all such cores regardless of the particular magnitude of the molding pressure. This method may be used for comminuted ferromagnetic materials molded at any pressure, providing the mechanical properties of the resultant cores meet the requirements. However, the temperature and time factors may require some variation, as a function of the materials used and the method of preparation. The amount of resin may also be varied, but it should remain a small percentage to insure that the particles remain together after heating.

Heat treatment may be provided in any suitable manner. There exists the possibility of utilizing an induction heating process instead of the usual oven heating. The former would allow the heat treatment to be done within a few seconds or, at the most, a very few minutes, since there would be no heat penetration problem. Also, the product should be more uniform when treated by the induction heating process. Frequencies in the range between 10,000 and 10,000,000 cycles should be useful for this process. A value of 500,000 cycles should be an excellent frequency compromise to provide uniform rapid action.

While we have indicated and described a system for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing I Number from the scope of our invention.

What we claim is:

l. A core consisting essentially of a compressed body of finely comminuted magnetic material containing about 0.67% intermingled free carbon, and some of said magnetic material being in sintered form.

2. A core according to claim 1 in which some of said magnetic material is in oxidized form.

3. A method of making an electrical circuit element comprising mixing a powdered magnetic material with about 0.75 of its weight of a resinous binding material, molding said mixture under high pressure to form a coherent body, curing said molded body below the decomposition temperature of said resinous material, and then heating said cured body at a temperature of about 800-900 F. for a period of time suflicient to carbonize said resinous material.

4. A method in accordance with claim 3 wherein said temperature and said heating time are sufficient to at least partially sinter the magnetic material.

ALBERT W. FRIEND. ARTHUR T. HARDING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,669,643 Andrews et al May 15, 1928 1,669,646 Bandur May 15, 1928 1,845,113 Andrews et al Feb. 16, 1932 1,845,144 Gillis Feb. 16, 1932 1,881,711 Lathrop Oct. 11, 1932 2,268,782 Stier Jan. 6, 1942 2,330,590 Kaschke Sept. 28, 1943 2,339,137 Berge Jan. 11, 1944 2,386,544 Crowley Oct. 9, 1945 

1. A CORE CONSISTING ESSENTIALLY OF A COMPRESSED BODY OF FINELY COMMINUTED MAGNETIC MATERIAL CONTAINING ABOUT 0.67% INTERMINGLED FREE CARBON, AND SOME OF SAID MAGNETIC MATERIAL BEING IN SINTERED FORM. 